Stem cells are unspecialized cells that self-renew for long periods through cell division, and can be induced to differentiate into cells with specialized functions, i.e., differentiated cells. These qualities give stem cells great promise for use in therapeutic applications to replace damaged cells and tissue in various medical conditions. Embryonic stem (ES) cells are derived from the blastocyst of an early stage embryo and have the potential to develop into endoderm, ectoderm, and mesoderm (the three germ layers) (i.e., they are “pluripotent”). In vitro, ES cells tend to spontaneously differentiate into various types of tissues, and the control of their direction of differentiation can be challenging. There are unresolved ethical concerns that are associated with the destruction of embryos in order to harvest human ES cells. These problems limit their availability for research and therapeutic applications.
Adult stem (AS) cells are found among differentiated tissues. Stem cells obtained from adult tissues typically have the potential to form a more limited spectrum of cells (i.e., “multipotent”), and typically only differentiate into the cell types of the tissues in which they are found, though recent reports have shown some plasticity in certain types of AS cells. They also generally have a limited proliferation potential.
Induced pluripotent stem cells (iPSC or iPSCs) are produced by laboratory methods from differentiated adult cells. iPSCs are widely recognized as important tools, e.g., for conducting medical research. Heretofore, the technology for producing iPSCs has been time-consuming and labor-intensive. Differentiated adult cells, e.g., fibroblasts, are reprogrammed, cultured, and allowed to form individual colonies which represent unique clones. Previously, identifying these types of cells has been difficult because the majority of the cells are not fully-reprogrammed iPSC clones. The standard is for iPSC clones to be selected based on the morphology of the cells, with desirable colonies possessing sharply demarcated borders containing cells with a high nuclear-to-cytoplasmic ratio. When clones are identified, they are manually-picked by micro-thin glass tools and cultured on “feeder” layers of cells typically, murine embryonic fibroblasts (MEFs). This step is performed typically at 14-21 days post-infection with a reprogramming vector. Then the clones are expanded for another 14-21 days or more, prior to undergoing molecular characterization.
Others have focused on developing techniques to rapidly and more accurately identify and characterize fully-reprogrammed adult fibroblasts and their downstream differentiation potential (Bock et al., 2011, Cell 144: 439-452; Boulting et al., 2011, Nat Biotechnol 29: 279-286). Also see, for example, co-owned U.S. Ser. No. 13/159,030, filed on Jun. 13, 2011, describing the use of Fluorescence Activated Cell Sorting (FACS) to identify and live sort unique subpopulations of stem cells as defined by unique expression patterns of surface proteins.
Thus, stem cells are an attractive source of cells for therapeutic applications, medical research, pharmaceutical testing, and the like. However, there remains a longstanding need in the art for an automated system for rapidly producing and isolating reproducible iPSC cell lines under standard conditions in order to meet these and other needs. There also there remains in the art a need for methods of making panels of iPSC cell lines, and differentiated cells produced therefrom, that are derived from multiple different individuals in a “population of interest.”